1. Field of the Invention
The present invention relates to a method of switching print modes of a printing device that as a plurality of different print modes for printing at different speeds.
2. Description of the Related Art
There has been known a print device including a hammer bank that is reciprocally transported to form an image on a recording medium, such as a recording sheet. Dot line printers and shuttle printers are representative examples of such print devices. Several types of shuttle mechanisms are known for reciprocally transporting the hammer bank. For example, one type of mechanism is provided with a cam or a link mechanism for converting rotational drive of a drive motor into linear movement. Another type of mechanism reverses the transport direction of the hammer bank by changing rotational direction of a drive motor. There is also known a direct drive type mechanism including a linear motor. The direct drive type mechanism requires no transmission mechanism for transmitting drive of the linear motor to the hammer bank.
FIG. 1 shows an example of a printing unit of a print device. In FIG. 1, the printing unit 1 includes a shuttle mechanism 2, a hammer bank 3, a sensor 4, and a shuttle drive mechanism. The shuttle mechanism 2 includes a guide shaft 11, direct drive bearings 12, a linear motor 20, and an inversion mechanism 30. The shuttle drive mechanism includes a controller 50, a shuttle control circuit 60, and a shuttle drive circuit 70. The guide shaft 11 extends leftward and rightward as viewed in FIG. 1. The direct drive bearings 12 are reciprocally movably mounted on the guide shaft 11. The hammer bank 3 is supported on the direct drive bearings 12, and so is reciprocally movable with the direct drive bearings 12. Although not shown in the drawings, the hammer bank 3 is provided with a plurality of printing hammers for forming a dot pattern on a recording medium based on print data received from an external device. The linear motor 20 is provided with a coil 21 and magnets (not shown), and is driven in a well known manner. Although not shown in the drawings, the coil 21 includes a reversing coil and a constant velocity coil. The inversion mechanism 30 has a pair of timing pulleys 32 and a timing belt 31 wound around the timing pulleys 32. The coil 21 is connected to the direct drive bearings 12 via the inversion mechanism 30. With this configuration, the drive force of the linear motor 20 is transmitted to the direct drive bearings 12 so as to reciprocally transport the direct drive bearings 12. The coil 21 is also reciprocally transported in synchronization with the direct drive bearings 12, but always in a direction opposite to the direction in which the direct drive bearings 12 are transported. In this way, the coil 21 serves as a counter balance. That is, when the direct drive bearings 12 with the hammer bank 3 mounted thereon are reciprocally transported, such a reciprocal movement of the coil 21, which has a fixed weight, achieves leftward and rightward weight balance of the print device, thereby reducing vibration generated on the print device due to the transport of the direct drive bearings 12.
The sensor 4 is provided near a movable portion, which in the present example is on the hammer bank side, for detecting a position of the hammer bank 3. The shuttle drive circuit 70 energizes the coil 21 by supplying an driving current, and the shuttle control circuit 60 controls the amount of driving current supplied to the coil 21. Based on positional information supplied by detection by the sensor 4, the controller 50 controls the shuttle control circuit 60 and the shuttle drive circuit 70 to move the hammer bank 3 in a predetermined shuttle speed pattern which is graphically shown in FIG. 3. The controller 50 also receives a variety of signals from an external device (not shown).
FIG. 2 shows a sheet transport mechanism 80 provided to the printing unit 1. A platen 81 is rotatably supported on a printer frame (now shown). A pair of left and right pin tractors 82 are provided for transporting a sheet S on the platen 81 in a direction perpendicular to the reciprocal movement direction of the hammer bank 3. The platen 81 and the pin tractor 82 are driven by a sheet feed motor 83. An ink ribbon 84 is provided for supplying ink.
As shown in FIG. 3, a region of the reciprocal movement of the hammer bank 3 (reciprocal movement of the hammer bank 3 will be referred to as xe2x80x9cshuttlexe2x80x9d hereinafter) includes a constant velocity region and reversing regions. In the constant velocity region, the constant velocity coil is energized so the shuttle moves at a constant speed. On the other hand, in the reversing regions, the reversing coil is energized, so the shuttle accelerates or decelerates. When the shuttle enters the reversing region from the constant velocity region, the shuttle gradually decelerates, and the velocity of the shuttle reaches zero at a reversing position P0. Then, the movement direction of the shuttle is reversed. The shuttle gradually accelerates in the opposite direction until the shuttle again enters the constant velocity region.
Depending on the type of character to be printed, some printing devices switch print modes with different print speeds. For example, a high speed print mode is used for printing normal characters at a high print speed. The high print speed in the high speed print mode is achieved by sacrificing quality of printed characters, which is determined by print dot density. On the other hand, a high quality print mode (i.e., a low speed print mode) is used for printing high-quality characters, such as bar codes images and OCR images. In the high quality mode, print speed is sacrificed for increased print dot density.
Conventionally, there have been two different methods for changing print speeds during printing operations upon switching print modes. According to a first method, the printing operations and the shuttle are both temporarily stopped. Then, the shuttle is restarted. Once a target shuttle speed is attained, printing operations are restarted. On the other hand, according to a second method, shuttle is continued while printing operations are temporarily stopped. Then, the value of the driving current supplied to the coil 21 is gradually changed, thereby gradually changing the shuttle speed. Once the target shuttle speed is obtained, then printing operations are restarted.
It should be noted that the series of operations for gradually changing the shuttle speed until a target speed is attained are called initialization operations.
Different accelerations and decelerations of the shuttle in the reversing regions may be used depend on the print speed. Also, the reciprocal movement distance of the shuttle may also be varied depending on print speed to enhance stability of control. When the reciprocal movement distance is changed, there is need to temporarily stop the shuttle, move the hammer bank 3 to an objective reversing position, and then restart the shuttle.
Also, in order to improve speed of printing operations, there has been proposed a printing device with a different configuration. For example, a printing device 1xe2x80x2 shown in FIG. 4 is substantially the same as the printing device 1, but the shuttle movement is controlled using the constant velocity coil and springs 40 without using the reversing coil. The springs 40 are provided at both ends of the guide shaft 11 and at both ends of the coil 21 for urging the hammer bank 3 and the coil 21.
Next, control of the shuttle movement in the printing device 1xe2x80x2 will be described. In the constant velocity region, an driving current is supplied to the constant velocity coil, thereby attaining shuttle of a constant velocity. When the hammer bank 3 enters the reversing region, application of the driving current to the constant velocity coil is stopped. The shuttle gradually decelerates while pressing the spring 40, and the velocity of the shuttle reaches zero at a reversing point. The direction of the velocity is then reversed, and shuttle accelerates in the opposite direction because of the urging force of the compressed spring 40. Upon entering the constant velocity region, the driving current is supplied to the constant velocity coil, and shuttle restarts at a constant speed.
The shuttle speed in the printing device 1xe2x80x2 is changed using the initialization operations. Specifically, upon receiving a print mode switching signal, printing operations are temporarily stopped while the shuttle movement is maintained. When switching from the low speed print mode to the high speed print mode, as shown in FIG. 5, the value of the driving current applied to the constant velocity coil is increased at the end of the constant velocity region. This increases the shuttle speed, and hammer bank 3 presses the spring 40 with an increased energy. As a result, repulsive force of the spring 40 is increased, thereby increasing the shuttle speed. This operation is repeated until the shuttle speed reaches an objective speed. Upon attaining the objective speed, the value of the driving current to the constant velocity coil is leveled, and the printing operations are restarted.
On the other hand, when switching from the high speed print mode to the low speed print mode, the value of the driving current at the end of the constant velocity region is decreased, thereby decreasing repulsive force of the spring 40. Then, the shuttle speed is gradually decreased until an objective shuttle speed is attained.
The reason for temporally stopping the printing operations during the initialization operations is that overshoot and variation on the shuttle speed occur due to unstable shuttle movement during the initialization operations. Overshoot indicates a situation where the shuttle speed increases to an excessively high speed for an instant at the beginning of the constant velocity region.
FIG. 6 shows a print pattern 100 printed on a recording sheet 5000. The print pattern 100 includes a normal text print region 1000, an OCR text print region 2000, and a bar-code print region 3000. All characters and text included in the print pattern 100 can be printed at the same print speed. However, in order to increase overall print speed, first the print of the normal text print region 1000 is completed in the high speed print mode, and then the print mode is switched to the low speed print mode using one of the above-described conventional methods. Then, the OCR text print region 2000 and the bar-code text print region 3000 are printed in the low speed print mode.
However, switching the print modes takes time when the shuttle must be temporarily stopped or initialization operations must be performed. Therefore, when only a small portion of the total print amount is printed in the high speed print mode, the overall print speed can even be reduced to slower than if only the low speed print mode was used.
It is objective of the present invention to overcome the above-described problems and also to provide a control method for quickly switching print modes of a printing device without stopping printing operations, thereby enhancing throughput of the printing device.
It is another objective of the present invention to provide a control method capable of improving throughput by continuing printing operations during initialization operations.
In order to achieve the above and other objectives, there is provided a switching method of switching print modes of a printing device including a print mechanism for performing printing operations while reciprocally moving relative to a recording medium. The reciprocal movement of the print mechanism is controlled using a coil including a reversing coil and a constant velocity coil. The switching method includes the steps of a) performing printing operations in a first print mode while reciprocally moving the print mechanism by applying a first driving current to the coil, b) receiving a signal indicating to switch from the first print mode to a second print mode different in a printing speed from the first print mode, and c) changing the first driving current to a second driving current to the coil to thereby switch from the first print mode to the second print mode, the printing operations and reciprocal movement of the print mechanism being continued during switching of the print mode.
There is also provided a switching method of switching print modes of a printing device including a print mechanism for performing printing operations while reciprocally moving relative to a recording medium. The reciprocal movement of the print mechanism is controlled using a constant velocity coil and an urging mechanism. The switching method includes the steps of a) performing printing operations in a first print mode while reciprocally moving the print mechanism by applying a first driving current to the constant velocity coil, b) receiving a signal indicating to switch from the first print mode to a second print mode different in a print speed from the first print mode, and c) if the first print mode is a low speed print mode and the second print mode is a high speed print mode, changing the first driving current to a second driving current, thereby switching from the first print mode to the second print mode, the printing operations and reciprocal movement of the print mechanism being continued during switching of the print mode.